Solar PV Inverters

Content

Role of Inverters Types of PV Inverters Component of Inverter & Working Principal Reading and Interpreting Inverter Specification Identifying Suitable Inverter Specification ? Inverter connection in PV System

Question

• Can you power a household fan by using just a battery?

Battery Load

Used to power sources appliances in cars, trains, etc.

Most common source – Battery.

The voltage is constantly steady.

The DC does not change its direction in time.

In DC, charge only flows from a source and not back to source.

Direct Current

• Play slideshow to see the waveform in detail.

• Used by household appliances like fan, tube light,fridge, etc.

• Most common source – Grid Supply.

• The voltage between two tips constantly changes.

• The current changes its direction in time.

• In AC, charge flows back and forth from a source.

Alternating Current

DC to AC Inverters

Cons

tant

Vo

ltage

Direct Current (DC)

Full Sine Wave

Half Sine WaveAlternating Current (AC)

Why Inverters?

Power source such as PV panels generate DC power

It is obvious that we cannot use DC to power appliances in our homes.

We need an instrument that can convert DC into usable AC.

An inverter converts DC to AC and vice versa.

Objective

• To be able to identify different types inverter based on output waveform and

functionality.

Solar Inverter – Types based on Output Waveform

These are the inverters whose output wave type is near topure sine.

There is difference between the grid voltage and this inverteroutput.

Distorted Sine Wave power Inverters

Solar Inverter – Types based on Output Waveform

These are the inverters whose output wave type is near topure sine.

There is no difference between the grid voltage and thisinverter output.

If they have the necessary electronic hardware, they can beconnected to the grid online.

In all grid tie inverters, this wave technology is used.

In the picture below, you can see true sine waveform.

Sine Wave power Inverters

Solar Inverter – Types based on Output Waveform

This is the inverter type which gives square output waves.

This is the cheapest and easiest inverting process.

Square wave output can make almost all grid devices workbetween 50 – 60 Hz.

But there is a possibility that this inverter may harm thesedevices if used long-term.

In the picture below, you can see 110V AC square waveoutput.

Square wave solar inverters

Activity

Match different load components to a suitable inverter type

Load Inverter Type

Computer/ Laptop

Pure sine wave

Square Wave

Distorted Sine wave

Incandescent Bulb

Fan

Audio Player

Water Heater

Refrigerator

LED / LCD TV

Printers

Objective Achieved

• We now understand the difference between sine wave, distorted sine wave and square wave

inverter.

Solar Inverter – Introduction

The main function of solar inverters is to change the DC system which is stored in accumulators and batteries into AC system which is used by devices that work through grid.

In short, it provides the transformation from DC to AC.

Shown here are some of the solar inverters.

DC Input AC Output

Sola

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Solar Inverter – DC to AC Converter Unit

• The voltage comes as DC to the system and is converted into AC by meansof transistors and other electronic components.

• Other components include unsynchronized MOSFET and BJT transistors orspecial integrated circuits.

• They produce voltages changing between -V and +V periodically.

• Play slideshow to see this conversion process in detail.

Rectifier

Converts AC input to DC

Uses four Diodes in bridge arrangement to achieve fullwave rectification Capacitor in parallel to load smoothensthe output waveform

• Higher the capacitance value, smoother the outputwaveform will be

• Capacitor Working Voltage should be higher then NoLoad Output Voltage value of Capacitor

Solar Inverter: Amplifier Unit

• Transformers are used in power inverters in order to increase the voltage.

• They are used in AC systems since they work with the magnetic currentprinciple.

• The necessary AC voltage required to make transformers work, which isproduced in the first unit, is transmitted to this area.

• Here, AC voltage is converted into 110V or 220V which are the parallel to gridvalues.

• In the picture below, you can see how a transformer unit works.

Solar Inverter and Normal Inverter – Difference

Can we use normal inverter in place of solar inverter? If yes, what changes are required?

Solar Inverter and Normal Inverter – Difference

Can we use normal inverter in place of solar inverter? If yes, what changes are required?

• There are no major differences between the two.

• Some companies manufacture their products as solar powerinverters (by introducing minor changes in existing inverters).

• The working structure and functions of normal inverters and solarinverters are the same.

• You can use normal power inverters with solar panel systemseasily.

• The most important thing is to make sure the solar panel system'soutput voltage is the same as the power inverter's input voltage.

Solar Inverter Components

Internal Circuit Diagram of Solar Inverters

Matching mechanism for inverter output ac waveform with grid power ac waveform

The inverter consists of mainly three components

1) Charge controller • Controls charge rate of battery (controlling flow

of charges)• Prevents battery from overcharging & supplies

adequate power for uncharged battery• Prevents back flow of power to PV at night to

ensure no power wastage2) Inverter• Converts DC into AC• to give power from Solar/Battery DC to Output

AC Power3) Isolation Transformer Provides Output

Isolation4) Grid-Tied• Consists of isolators and circuit-breakers• Grid Charger to Charge Battery while

Emergency

Solar Inverter – Working Principle

1. SOLAR PV charging batteries andfeeding power to the load. In case ofsolar unavailability, load is fed byBattery.

2. If solar not available and battery goeslow, inverter connects to the grid andcharges the battery as well as feedsload.

Solar Inverter – Working Principle

Principle can be explained using H-Bridge diagram (following slides)

Circuit DiagramH-Bridge

DC to AC

DC to AC

Transistor StateQ1 OFFQ2 ONQ3 OFFQ4 ON

Transistor StateQ1 ONQ2 OFFQ3 ONQ4 OFF

Solar Inverter – Input and Output Voltage

We know that solar inverters make DC to AC voltage conversion.

Inverters output voltages are the same with the necessary input voltage values for the electronic devices that are sold to work.

Their intended use is to take the DC voltage which is found in solar panels or batteries and convert it into AC voltage that these devices can use.

Power Inverter Output Voltages: City grid voltages have values such as 110V, 115V, 120V, 220V and 240V around the world. That's why the power inverters that are produced have AC outputs which have these voltage values.

Power Inverter Input Voltages: Input voltages are DC and they differ a lot. There are power inverters which have input voltages between 6V – 48V.

Solar Inverter – Types

Choosing right Solar Inverter

• Stand-aloneOff grid solar panels system is an independent installation that is notconnected directly to the utility feed. You use battery to stock the energy.

• Grid-tiedOn grid solar panels system is an installation connected directly to theutility feed. If the installation produces more electricity than needed thenthe excess power is sold to the electric company.

Stand-Alone Inverters

Can the battery be charged by grid and PV both, simultaneously?

Off grid solar PV systems generate electric power for local consumption. It can power the domestic/local electric loads and can charge the battery

• Off grid inverter draws DC energy from batteries charged by PV arrays, and converts it into ac power to be further supplied to the loads

• Stand alone inverters allows the battery to be charged by PV panels as well as Grid Power

Stand-Alone Inverters – Working Principle

• Off – Grid Solar power solution consists, Solar PV Panels, Solar Powerconditioning unit (PCU), batteries, mounting structures and other accessories.

• The solar charge Controller which is inbuilt in PCU will convert theuncontrolled DC in the constant DC to Charge the batteries and to feed toinverter.

• The PCU continuously monitors the state of Battery voltage, Solar Poweroutput and the loads.

• To maximize the usage of solar power, When the Battery voltage falls below apre-set level, the PCU will automatically transfer the Load to Grid / DG powerand also charge the batteries via grid.

• Once the Batteries are charged to pre-set level, the PCU cuts off the Grid/DGPower from the system and will restore of feeding the loads from the batterybank & also restore to charging the battery from the available solar power.

• The PCU always gives preference to the Solar Power and will Use Grid / DGpower only when the Solar Power / Battery charger is insufficient to meet theLoad requirement.

* Electrifying school, health centers in remote areas

* Rural Village Electrification

* Emergency lighting & communication systems

* Electrification of small shops and homes

* Electrification of small office and home office

* Electrification of rural banking branches & ATMs

Stand-Alone Inverters – Applications

Solar Grid-Tie Inverter

How can the grid line be used to feed power back to the grid?

• Convert Direct Current from PV Arrays into Alternating Current with voltage and frequency matching with that of grid power

• Inverter output and gird input are connected in parallel to the loads

• The loads draw power from the PV (inverter)

• The excess power generated can be fed back to the grid

• Prevents connected loads from damage due to short-circuit, shocks, over-loading, power surge, etc.

Solar Grid-Tie Inverter: Working Principle

• A “grid-tie” (sometimes referred as utility/ grid interactive) solarsystem is one that ties into the power grid, pulling electricityfrom the grid when then pushing excess electricity back into thegrid when the local customer isn’t using the full capacity beinggenerated by the PV panels (photovoltaic).

• This is the simplest and most cost effective PV design for mostof the sites where power is reliable and stable.

• Because of the very fact that these systems are tied into thegrid, it follows the safety feature of disconnecting the systemfrom the grid when grid goes down.

• The systems does not provide backup power during a powercuts (even if the sun is shining). But for the sites with reliablegrid power and the day time usage are high, this is usuallylogical and economically viable system choice.

Corporate houses with high day time load

Schools and Colleges

Industries with day time peak load

Industries with RPO obligations

Small office & home office

Commercial complexes & software parks

Solar Grid-Tie Inverter – Applications

• While Grid-Tie works with the grid online, stand-alone systems work separately from the grid.

• While grid-tie inverter outputs are full sine, stand-alone inverters can produce outputs such assquare, modified sine or true sine. Almost all electronic devices that work with AC voltage canwork with these wave outputs.

• Since grid tie inverters have more complex electronic systems, they are more expensive thanstand-alone inverters which actually have the same features.

• You can find grid tie inverters in the market with more power and voltage options. It is a morecommonly used product.

• You can collect the electricity that you give to the grid with grid tie inverters, from the government.There are many legal regulations and incentives in America, Britain, France and many othercountries regarding this issue.

Grid-Tie and Stand-Alone Inverter – Difference

1. Square wave solar inverters• This is the inverter type which gives square output

waves.• This is the cheapest and easiest inverting process.• Square wave output can make almost all grid

devices work between 50 – 60 Hz.• But there is a possibility that this inverter may harm

these devices if used long-term.• In the picture below, you can see 110V AC square

wave output.

Solar Inverter – Types based on Output Waveform

2. Modified Sine Wave power Inverters• Output wave is square but it undergoes a special

process to make it more similar to sine.• Modified sine wave is a more commonly used method

than square wave.• It can make all AC devices work.• You can't connect such devices to the grid online

because grid voltage is pure sine.• In the picture below, you can see modified sine

waveform.

Solar Inverter – Types based on Output Waveform

3. True Sine Wave power Inverters• These are the inverters whose output wave type is pure

sine.• There is no difference between the grid voltage and this

inverter output.• If they have the necessary electronic hardware, they can

be connected to the grid online.• In all grid tie inverters, this wave technology is used.• In the picture below, you can see true sine waveform.

Solar Inverter – Types based on Output Waveform

Solar Inverter – Protection Systems

1. Over temperature shutdown

2. Surge handling capacity

3. Automatic Overload Protection

4. Ground Fault Protection

5. Short Circuit Protection

According to their production technologies, solar power inverters can include many different protection systems. The most well-known protection systems are:

1. Over temperature shutdown• They are also known as thermal protection systems.• When a power inverter converts power over the capacity it

has or at values very close to this capacity it may overheatand break down.

• Electronic parts generally start to break down over 90C.• In order to prevent this from happening, heat sensitive

sensors are placed inside the power inverters, and thisenables shutdowns at high temperatures or decrease ofthe power transmitted.

• These parts called PTC or NTC send the necessarytemperature information to the central processing unitwhen high temperatures are reached and this activates theprotection.

Solar Inverter – Protection Systems

2. Surge Handling Capacity• While starting, an appliances requires about x times its

actual power requirement.• For example, an AC would require great amount of current

while getting started and then goes on to its normalcurrent consumption.

• So, we need something that can protect the inverter fromsuch surge in load requirement.

• A surge protector (or surge suppressor) is an appliancedesigned to protect electrical devices from voltage spikes.

• A surge protector attempts to limit the voltage supplied toan electric device by either blocking or by shorting toground any unwanted voltages above a safe threshold.

• Other than overload, a Surge Protection System also takescare of aspects such as lightning to mitigate the risk.

Solar Inverter – Protection Systems

3. Automatic Overload Protection• Overload protection works in order to prevent

breakdowns caused by burns of the parts which arecaused by power load which exceeds the capacity ofthe device.

• For example, if an inverter which has 4000W capacityis loaded with 4300W power, The protection system is activated and Gives the necessary warning to the user Warnings include closing the device and

decreasing the transferred power.

Solar Inverter – Protection Systems

4. Ground Fault Protection• In high capacity solar cell power inverters, grounding

systems are essential. • In order to protect the devices that are connected to the

system and in order for the inverter to work more efficiently, the grounding should be done properly.

• If a high capacity power inverter has not been grounded properly, by means of the protection system that it has inside, it will warn the user and carry out the necessary processes.

• If grounding is not done properly, ground, not short circuit connection is carried out automatically and thus the system is protected.

Solar Inverter – Protection Systems

5. Short Circuit Protection• By means of this protection system, the short circuit problem

which is caused by the output cables touching one anotherdue to user misuse is prevented.

• During short circuit, the device is immediately put on passivecondition and is shut down.

• Other names for this protection system are known as ACOvercurrent protection and DC Overcurrent protection.

Solar Inverter – Protection Systems

• Some power inverters have special software which allowsthem to be monitored and controlled remotely.

• The data on the power inverter can be read and theinverter can be controlled over the internet or broadbandnetwork and via computers or smart phones.

• Most data such as total power, input voltage, outputvoltage, working time, malfunctions or faults can bemonitored remotely.

• In the picture, an inverter monitoring system can be seenin detail.

Solar Inverter – Monitoring System

Choosing Solar Inverter

Factors:• How much power do you need?• What is your solar panel power output?• How is load distributed?• What is Performance/price values?• What production technology is used?.• Manufacturing company’s background/profile.• Output Waveform

IEC for Solar Inverters

• Determines Standard procedure & parameters forManufacturers to determine efficiency of SolarPower Conditioners which is based on certainparameters.

IEC for Solar Inverters

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